1. Field of the Invention
This invention relates to the use of thermostatic HVAC controls that are connected to a computer network as a part of a system for offering peak demand reduction to electric utilities. More specifically, the present invention pertains to use of communicating thermostat combined with a computer network to verify that demand reduction has occurred.
2. Background
Climate control systems such as heating and cooling systems for buildings (heating, ventilation and cooling, or HVAC systems) have been controlled for decades by thermostats. At the most basic level, a thermostat includes a means to allow a user to set a desired temperature, a means to sense actual temperature, and a means to signal the heating and/or cooling devices to turn on or off in order to try to change the actual temperature to equal the desired temperature. The most basic versions of thermostats use components such as a coiled bi-metallic spring to measure actual temperature and a mercury switch that opens or completes a circuit when the spring coils or uncoils with temperature changes. More recently, electronic digital thermostats have become prevalent. These thermostats use solid-state devices such as thermistors or thermal diodes to measure temperature, and microprocessor-based circuitry to control the switch and to store and operate based upon user-determined protocols for temperature vs. time.
These programmable thermostats generally offer a very restrictive user interface, limited by the cost of the devices, the limited real estate of the small wall-mounted boxes, and the inability to take into account more than two variables: the desired temperature set by the user, and the ambient temperature sensed by the thermostat. Users can generally only set one series of commands per day, and to change one parameter (e.g., to change the late-night temperature) the user often has to cycle through several other parameters by repeatedly pressing one or two buttons.
As both the cost of energy and the demand for electricity have increased, utilities supplying electricity increasingly face unpleasant choices. The demand for electricity is not smooth over time. In so-called “summer peaking” locations, on the hottest days of the year, peak loads may be twice as high as average loads. During such peak load periods (generally in the late afternoon), air conditioning can be the largest single element of demand.
Utilities and their customers generally see reductions of supply (brownouts and blackouts) as an unacceptable outcome. But their other options can be almost as distasteful. In the long term, they can build additional generating capacity, but that approach is very expensive given the fact that such capacity may be needed for only a few hours a year. And this option is of course unavailable in the short term. When confronted with an immediate potential shortfall, a utility may have reserve capacity it can choose to bring online. But because utilities are assumed to try to operate as efficiently as possible, the reserve capacity is likely to be the least efficient and most expensive and/or more polluting plants to operate. Alternatively, the utility may seek to purchase additional power on the open market. But the spot market for electricity, which cannot efficiently be stored, is extremely volatile, which means that spot prices during peak events may be as much as 10× the average price.
More recently, many utilities have begun to enter into agreements with certain customers to reduce demand, as opposed to increasing supply. In essence, these customers agree to reduce usage during a few critical periods in exchange for incentives from the utility. Those incentives may take the form of a fixed contract payment in exchange for the right to cut the amount of power supplied at specified times, or a reduced overall price per kilowatt-hour, or a rebate each time power is reduced, or some other method.
The bulk of these peak demand reduction (PDR) contracts have been entered into with large commercial and industrial customers. This bias is in large part due to the fact that transaction costs are much lower today for a single contract with a factory that can offer demand reduction of 50 megawatts than they would be for the equivalent from residential customers—it could take 25,000 or more homes to equal that reduction if these homes went without air conditioning.
But residential air conditioning is the largest single component of peak demand in California, and is a large percentage in many other places. There are numerous reasons why it would be economically advantageous to deploy PDR in the residential market. Whereas cutting energy consumption at a large factory could require shutting down or curtailing production, which has direct economic costs, cutting consumption for a couple of hours in residences is likely to have no economic cost, and may only result in minor discomfort—or none at all if no one is at home at the time.
Residential PDR has been attempted. But there have been numerous command and control issues with these implementations. The standard approach to residential PDR has been to attach a radio-controlled switch to the control circuitry located outside the dwelling. These switches are designed to receive a signal from a transmitter that signals the compressor to shut off during a PDR call.
There are a number of technical complications with this approach. There is some evidence that “hard cycling” the compressor in this manner can damage the air conditioning system. There are also serious issues resulting from the fact that the communication system is unidirectional. When utilities contract for PDR, they expect verification of compliance. One-way pagers allow the utility to send a signal that will shut of the NC, but the pager cannot confirm to the utility that the NC unit has in fact been shut off. If a consumer tampers with the system so that the NC can be used anyway, the utility will not be able to detect it, absent additional verification systems.
One way in which some utilities are seeking to address this issue is to combine the pager-controlled thermostat with so-called advanced metering infrastructure (AMI). This approach relies on the deployment of “smart meters”—electric meters that are more sophisticated than the traditional meter with its mechanical odometer mechanism for logging only cumulative energy use. Smart meters generally include a means for communicating instantaneous readings. That communication may in the form of a signal sent over the power lines themselves, or a wireless communication over a data network arranged by the utility. These meters allow utilities to accomplish a number of goals, including offering pricing that varies by time of day in order to encourage customers to move consumption away from peak demand hours. These smart meters can cost hundreds of dollars, however, and require both a “truck roll”—a visit from a trained service person—and most likely the scheduling of an appointment with the occupants, because swapping the meter will require turning off power to the house.
If the utility installs a smart meter at each house that contracts to participate in a PDR program, it may be possible to verify that the NC is in fact switched off. But this approach requires two separate pieces of hardware, two separate communications systems, and the ability to match them for verification purposes.
It would be desirable to have a system that could both implement and verify residential peak demand reduction with reduced expenses.